Arrangement for the degasification of plastic masses during their treatment by means of a continuous mixing and kneading worm



Feb. 6,1968 GRESCH 3,367,635 I ARRANGEMENT FOR THE ASIFICATION OFPLASTIC MASSES DURING THEIR TREATMENT BY MEANS OF A CONTINUOUS MIXINGAND KN ING WORM Filed Jan. 1966 nuni:

United States Patent ()fiice 3,367,635 ARRANGEMENT FOR THEDEGASIFICATION OF PLASTIC MASSES DURING THEIR TREATMENT BY MEANS OF ACONTINUOUS MIXING AND KNEADING WORM Walter Gresch, Lachmattstrasse 55,Muttenz, Switzerland Filed Jan. 26, 1966, Ser. No. 523.083 Claimspriority, application Switzerland, Feb. 8, 1965, 1,691/ 65 2 Claims.(Cl. 259-4) ABSTRACT OF THE DISCLOSURE A device for the degasificationof plastic masses during treatment in a continuous mixing and kneadingoperation wherein the plastic material is subjected to the action ofrotating and axially reciprocating interrupted conveyor worms. Thedevice includes at least one baflle ring of predetermined configurationfor maintaining the axial distance between the worm vane and the bafiiering constant.

The present invention relates to an arrangement for the degasificationof plastic masses during their treatment by means of a continuous mixingand kneading worm of which the shaft fitted with interrupted conveyorworm vanes carries out a to-and-fro movement as well as the rotation.

' In the preparation of plastic masses, such as for example of syntheticplastics materials, there is introduced a measured mixture of syntheticmaterial powder, colorant, plasticiser and filler into the treatmentarrangement, placed under pressure by the worm shaft and moved to theoutlet nozzle. During this treatment the stated ingredients are mixed,heated and often undergo a chemical change. During this it is importantthat the product emerging through the nozzle is homogeneous and free ofpores.

During the introduction of the various materials into the worm machineit is not possible to prevent that the introduced material includes airand steam pores. Further because of the chemical change during thepreparation gas-containing pores can result, which are undesired andmust be removed. In certain instances it is necessary to remove from thematerial relatively readily volatile solvent media in the viscous fluidphase.

An extraction of the gases and vapours by direct connection of a vacuumpump or by a connection with the atmosphere does not lead to success, asthe product is under pressure and as the small bubbles are surrounded bya thick layer of the viscous product so that they cannot break throughto the outer surface. For these reasons it has already been proposed touse a baffle ring which reduces the passage between the worm shaft andthe worm housing to a thin annular gap. The product emerges through thisgap in the form of a thin hose so that the gas and vapour bubbles ofsmall size can break through the thin layer and arrive at the outersurface. Directly after the bafile ring there is provided in the wormhousing an opening for the emergence of the gases which leads into theatmosphere or into a vacuum. The baffle ring can remain still in thehousing or be constructed on the shaft for rotation therewith. It isonly important that no dead spaces result in which particles of productremain at rest and thereby change colour or decompose chemically. Forthis purpose the bafile rings are assembled of two cones, the first conewith acute opening angle reducing the crosssection gradually and thesecond cone with obtuse angle enlarging the cross-section again veryrapidly.

If the worm shaft carries out only a rotation it is simple Patented Feb.6, 1968 to allow the ends of the worm vanes to move past so close to thecones that no dead space results. In machines of which the shaft inaddition to the rotary movement carries out an axial to-and-fro movementthis close moving past by the bafile ring cannot be achieved with simplemeans. Further in such worm machines there exists the problem of thefurther conveying of the product flowing out of the baflle ring withoutany undesired blockage in spite of the axial movement of the shaft. Sucha blockage would give rise to a thickening of the layer and thus ahindering of the emergence of the gas, whereby even an escape of thematerial through the vapour outlet slot can occur.

According to the invention it is now proposed that in the path ofmovement of the worm vanes is arranged at least one baffle ring of whichthe shape corresponds to the line of movement of the adjacent worm vaneso that the gap width determined by the axial distance between the wormvane and the baifie ring is constant.

It is important that the thin layer also remains intact behind thebaflle ring, and that also during the rearward movement of the shaft.The thin layer must not be broken up and dammed up, so that no materialcan escape through the degasification openings. For this purpose theconveying action of the worm in the region of and after thedegasification opening is increased. Suitably for the purpose behind thebattle ring in the interruptions of the worm vanes are insertedpassage-closing elements and the kneading teeth are removed, so thatclosed worm vanes result.

In the accompanying drawing an example of embodiment of the subject ofthe invention is represented, and there appear:

FIGURE 1 a vertical longitudinal section through the arrangement FIG. 2a vertical longitudinal section to an enlarged scale through a bafflering FIG. 3 a horizontal longitudinal section through the same bafflering and FIG. 4 variations of the cross-section of the bafile ring.

The arrangement comprises a driving device 1 which drives a worm shaft 2and simultaneously puts it into an axial to-and-fro movement. The wormshaft 2 is mounted in a housing 4, which has a charging hopper 3 andkneading bolts 5 and 5a. These bolts serving for the kneading operationare arranged distributed at the periphery of the housing and prevent arotation of the product. Further there are provided in the housing 4baffle rings 6, a gas removal connection piece 7 being provided aftereach baflle ring 6. The finished product passes out of the arrangementthrough the nozzle opening 8.

The worm shaft 2 is provided with interrupted worm vanes. The worm vanes9, 9', 9" have a large pitch, whilst the worm vanes 10, 10, 10" haveonly a small .pitch. Differences in the pitches are achieved in thateither the inclination is varied or the Worm is made with differentvanes. The interruption between the worm vanes permits the penetrationof the kneading bolts 5 and 5a.

The construction of the baffle rings in greater detail is visible inFIGURES 2 and 3. The bafile ring 6 is not made as a simple body ofrotation, but is so shaped that the same corresponds to the axialmovement of the worm shaft. It is now assumed that the beginning of theworm, which leads the product onwards from the baflle ring, has a middleposition at the top and after rotation reaches the extreme right-handposition. After rotation the lower middle position is less reached,after 270 rotation the extreme left-hand axial position is reached, andafter 360 rotation the initial position is reached again. The bafllering formed in accordance with the invention always has the same smallaxial distance from the start of the worm. Considered purelygeometrically the baffie ring can be divided into a number, for example360, of radial lamellas, of these lamellas the first and 180th, that isto say the top and the bottom lamellas are not displaced, whilst the90th and 270th corresponding to the end positions of the shaft aredisplaced in the axial direction to the maximum towards the right-handor towards the left-hand. The axial positions of the remaining lamellasare determined according to the intermediate positions of the shaft.

In FIGURE 2 with 4' is represented the rear part of the housing, whichsuitably for the purpose is divided in the vertical longitudinal planeand can be swung apart for the purpose of cleaning. The correspondingpart 6' of the bafiie ring is inserted directly in front of the gasremoval connection piece 7 in the housing part 4'. The end of the wormwith small pitch is represented in the upper and in the lower axialmiddle position and indicated with 9a and 9c respectively. With 10a and100 is illustrated the start of the worm with larger vane pitch in theupper middle position and in the lower middle position.

At the beginning of the rotation of the shaft the worm vane 9 is atfirst in the position 9a (top) and after 90 assumes the position 9b(FIG. 3) and further after 180 assumes the position 90. The position ofthe worm vane after 270 is indicated with 9d, whereupon the worm vanereturns again into the initial position 9a. Herein the bafile ring 6 isso shaped that the axial distance between the conical surfaces thereofand the bevelled ends of the worm remains the same in every shaftposition. Similarly the worm vane 10 assumes the position 10a, 10b, 10cand 10d, the distance between the baffle ring 6 and the worm vane 10being narrower in order to engage and drive on all the emerging productparticles.

In order to be able to drive on the product emerging from the bafflering without further blockage even when the shaft moves axiallybackwards towards the bafiie ring there are inserted in thedegasification zone two to three worm vanes of which the vane pitch isgreater than in front of the bafile ring. Further it is suitable toclose the interrupted vanes 9, 9" behind the gas extraction connectionpiece 7 by the insertion of vane closure elements 11 and to remove thecorresponding kneading bolts 5a. Thus the conveying action of the wormis increased.

After this zone of increased pitch the pressure must again be freshlybuilt up, and that by means of the following worm vanes which have onlya small pitch. The worm vanes are interrupted in order to permit thepenetration of the kneading teeth fixed in the housing and at the sametime to achieve a kneading action.

In operation the product is charged into the arrangement and first comesinto a zone of increased pitch, next into a zone of smaller pitch forthe creation of pressure and kneading throughout. Next there is effectedthe degasific-ation by means of the described baffle ring, whereby thepressure is freshly built up. The dega-sification can be effected onceor several times, in the latter instance several bafiie rings beingarranged one behind another.

In FIGURES 1 to 3 the baffle rings are represented in profile astriangles. However it is also possible that the baffle rings may haveother profiles, as can be seen from FIGURE 4. The four illustratedprofiles correspond to the respective axial shaft displacement throughthe toand-fro movement of the kneading worm.

What I claim is:

1. An arrangement for the degasification of plastic masses during theirtreatment by means of a continuous mixing and kneading device, saiddevice comprising a housing with an inlet opening and an outlet openingarranged on different ends of said housing and with a gas removalaperture in the middle of said housing; a worm shaft arranged in saidhousing being connected to a driving device to cause a rotation and areciprocating axial movement of said shaft; interrupted worm vanes beingarranged on said shaft and kneading bolts mounted in said housing; inthe path of movement of said worm vanes is arranged at least one bafflering of which the shape corresponds to the line of movement of theadjacent worm vane so that the gap width determined by the axialdistance between the worm vane and the baffle ring is constant.

2. An arrangement as claimed in claim 1, in which behind the baffle ringin the interruptions of the worm vanes are inserted vane closureelements and the kneading teeth are removed so that closed worm vanesresult.

References Cited UNITED STATES PATENTS 2,595,455 5/1952 Heston 18-122,970,341 2/1961 Mallory et al. 18-12 3,224,739 12/1965 Schuur 259-4WILLIAM I. PRICE, Primary Examiner.

J. M. BELL, Assistant Examiner.

